


Monster Mash

by Baronessbamf



Category: Voltron: Legendary Defender
Genre: Alien Sex, Anal Fingering, Anal Play, Anal Sex, Blow Jobs, Cloaca, Fluff and Smut, Keith has been REALLY lonely, Keith still loves Shiro, M/M, Monster sex, Monsters, Robeast!Shiro, Size Difference, Size Kink, Tender monster Fucking, Tongue Fucking, Transformation, Weird Biology, alien experiment, guys shiro is a robeast in this and he fucks keith, like no im serious no tags can warn you enough, minor medical stuff, sexy monsters
Language: English
Status: Completed
Published: 2016-10-31
Updated: 2016-10-31
Packaged: 2018-08-28 06:49:03
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,232
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/8435683
Author URL: https://archiveofourown.org/users/Baronessbamf/pseuds/Baronessbamf
Summary: “I don’t think it’s going to fit dude.” Keith deadpanned. Shiro laughed. “But I didn’t wait a year, drop out of military school, live in the desert, and rescue you you from a space wreck to not try...do you want to try?” He didn’t just mean about the monster dick. He meant in general, because there was no going back from this.
--Shiro is a Robeast and Keith still loves him anyway.





	

**Author's Note:**

> Happy Halloween! (Also Sorry!)

Shiro doesn’t remember much from his time with the Galra, he does remember pain. Fighting. Being scared. Needles. More pain. Being conscious when he’d rather have been unconscious. Being Unconscious when he’d rather have been conscious. He’d have went mad with the agony long ago if it weren’t for one memory keeping him sane.

_ Keith. _

_ Keith looks up at him. “You be safe now, don’t go getting into trouble.” _

_ “I’m going on this mission to keep everyone safe.” he remembers smiling at Keith. A goodbye kiss. Not goodbye,“Until we next meet.” _

Well today was Shiro was coming home. He’d planned this carefully. Pretend to be a dumb monster, as mad as all the other Robeasts. Then, when he was being transferred from one part of the station to another, Shiro made his escape.

He was a lot stronger and bigger than he used to be, this had it’s advantages, but he was easier to hit and subdue. But he wasn’t a mad wild animal scared by a few shocks and yells. He had a goal, that goal was home. To Keith.

Stealing the escape pod had been easy, piloting it; a little difficult, his hands were a lot bigger now. That's Probably why he crash landed.

 

****

 

Keith heard a loud sound out in the desert. In his gut, he knew instinctively.  _ It was Shiro _ . He got dressed and on his hovercycle. He had to get to Shiro before anyone else. The authorities would just...hide him away.

The wreck was mostly intact and Keith spent no time prying it open. He could hear the sounds of military vehicles in the distance. With his crowbar he pried the cockpit open and…

“Shiro?” Keith breath for a moment, shocked.

It was Shiro, you could see it in the face, his jawline now jutted unnaturally out to make room for the large fangs on the bottom row of teeth. He was broader now, maybe twice the size he used to be, 8 foot tall to boot. His skin, now a purple tinged to it stretched over his abnormally large physique. The skin had ripped in places revealing the pink muscle underneath. Both of Shiro’s arms were now metal and large. Too Long to stand upright surely? Was that a tail too?

But it was Shiro. He still looked like Shiro.  

“How the fuck am I going to get you back on my cycle?”

Keith didn’t know how, but he managed to get Shiro back to his shack. He even dragged Shiro onto his bed. Shiro really was something to behold now. Giant clawed feet and hands. Covered in battle scars.

Keith caressed his boyfriend’s jaw. “What happened to you?” This must have hurt Shiro, growing a tail can’t be painless. Some of Shiro’s hair had went white, that only happened under shock right? That Shiro had changed didn’t bother Keith, that Shiro had been in so much pain without Keith to help him?

That bothered him.

Keith decided to cook, if he’d been turned into a monster by space aliens. (it better be aliens otherwise all the stuff on his conspiracy board would be difficult to explain to Shiro) He’d want a decent meal. Keith should run Shiro a bath too. 

He threw some ingredients in his slow cooker and went outside to his heater to fill it with hot water. He’d need to find somewhere different for them to live. The military would catch on soon. Also this shack was too small for Shiro. Hopefully he could get a decent in-house water heater in his next middle-of-nowhere shack.

Keith busied himself doing domestic chores, checking in on Shiro every now and then.

He had just finished filling the bathtub when he heard a guttural groan from the bedroom. Keith was a little cautious, he’d been pleased his boyfriend was back but...nervous. What if Shiro wasn’t...Shiro anymore? Worse, what if Shiro was upset?

Keith entered his bedroom to see Shiro hunched over an old mirror. (Keith had got it out the trash.) Looking at his face. Shiro didn’t have much of a nose anymore, just nostrils and a little bump. Pointy (but furry) ears, and a set of bright yellow eyes. The sound Shiro made was displeased and he sat back on Keith’s bed, gently.

Yeah, that was still Shiro in there. All contained emotion, not outburst of animalistic anger. Keith felt his heart hurt.

“I er...I’m cooking some dinner. If you’re hungry.” Keith walked into the room and sat next to Shiro. “Or you could have a hot bath.” Sat next to him, it struck him how much Shiro now dwarfed him in size now.

Shiro appeared genuinely happy that Keith was here. Shiro’s lips made a wonky smile and he gave a...purr? Chuff? A happy sound.

“Can’t talk huh?” Shiro gave a whine in response and shook his head. Keith frowned, knelt up and kissed Shiro. Another chuff.

 

****

The bath was a little too hot for Shiro, so they let it to cool and ate dinner, which Shiro went to with some gusto, and Keith caught him up on what had happened to him. Dropping out...living in a shack...getting deep into alien conspiracy theories.

Shiro would make sounds, growls of agreements, barks of laughter...

Yeah, Keith could get used to this. Under all the monstrousness it was still kind, handsome Shiro. Shiro wasn’t even that grotesque he was pretty hot still and...Keith should stop that train of thought. I mean Shiro probably didn’t even have a...or if it was maybe it wouldn’t…

Keith coughed, “C’mon Shiro let's get you in the bath.” he voice cracked as he stood up to put the plates in the sink.

Shiro could just about sit in the bath but Keith had to help Shiro wash himself, since, those claws were not sponge friendly. Keith lathered and rinsed Shiro’s hair, helped brush his teeth, washed his back and chest.

When they were in the garrison together, they’d sometimes wash each other. Because it was intimate, sweet, romantic. Was this approaching those things? Shiro was making those chuffing sounds again. That meant he was relaxed, right? Keith supposed it was time to move down to clean Shiro’s...uh…

“Is that...a cloaca?” Keith shot a look into Shiro’s face, probably a look of shock. 

Shiro looked down at himself,shrugged, leaned back and gestured to Keith.  _ Why don’t we both find out?  _ He seemed to say.

Keith rolled up his sleeves and soaked his sponge. Shiro had a smallish opening there, and a bump of...something. He still very much had his balls. Which, cool.

Keith stroked the bump softly and Shiro gave a groan...growl…? Whatever the sound it sent shivers all the way down into Keith’s gut. Keith abandoned the sponge and rubbed with his palm, a bit firmer. Shiro made the same pleased sound.

Keith kept stroking the bump and cupped and caressed Shiro’s balls too. Shiro’s breath grew heavy and ragged until-

SLOOP!

Shiro’s dick was large, pink, swollen, and...spiney.

The two of them looked at each other, a little startled. Shiro’s breathing still ragged, his yellow eyes met Keith’s. Shiro looked worried, as if just truly aware how different he was now.

“I don’t think it’s going to fit dude.” Keith deadpanned. Shiro laughed. “But I didn’t wait a year, drop out of military school, live in the desert, and rescue you you from a space wreck to not try...do you want to try?” He didn’t just mean about the monster dick. He meant in general, because there was no going back from this.

Shiro nodded.

Keith pulled his shirt of, threw his boots and pants off, “Then get in the bedroom Shiro.”

 

****

With Shiro looming over him, Keith really did feel small now, especially with that giant dick waggling around. Was he scared? A little. Was that going to put him off? Hell no, this was the love of his life.

Shiro brushed his knuckles against Keith’s cheek. If Shiro could talk he might say;  _ “Are you sure about this?” _ or  _ “Don’t be scared.” _

Keith put his hand on Shiro’s holding it there on his cheek, “I’ll tell you if you’re hurting me, ok? I want this. I love you.” Keith leaned up to kiss Shiro on the...lower...jaw. Keith could handle the tail, abnormal size, and monster dick. But he was going to kissing Shiro properly. He sighed.

Shiro tilted his head curiously and opened his mouth.

“Wha-?” A long thick tongue slid out and licked Keith on the neck, “oh.” Keith ejected before giggling. Damn his ticklish neck. Then the tongue slid down lower to Keith’s chest and slowly, teasingly, over his nipples. Keith moaned.

Further down still, Shiro’s tongue went. Wrapping around Keith’s cock. Wet, firm and thick. Keith bucked upward and groaned. Shiro’s tongue undulated and swirled around his cock and Keith could feel his cheeks turn hot and his orgasm build. He bucked wildly and Shiro gathered him in his giant hands, pulling him close. “S-shiro!” Keith panted before he came.

Shiro’s tongue slid slowly back into his mouth. So maybe Keith could cope with no more deep kisses.

Keith lay quiet for awhile, catching his breath. Shiro nudged him softly with his head. “Shiro...I’m going to prep myself now.” Keith leaned down and fished his bottle of lube from under his bed. He was going to need the whole bottle. Like. Yeah.

He squirted a good amount onto his hand, got on his knees and leaned over so Shiro could get a good look-see. Keith took a deep breath a slid one of his fingers in, then another. He’d done this before and wasn’t out of practice. The year in the desert had been lonely, but if he’d known Shiro would come back to him like this…

Well he would have bought a much larger dildo that's for sure.

Keith put a third finger in stretching himself as much as he could but...he needed something bigger. He sighed half aroused half frustrated. Shiro growled a little too and gabbed the bottle of lube.

“Do you want my help to-” Keith was cut of my Shiro bit the lid of the bottle off and poured a friendly amount on his own hands and cock. Shiro took one of large fingers and slowly slid it into Keith. “Oh. ok. That should work.” he groaned, his eyes fluttering shut. He already felt so full, he couldn’t imagine having all of Shiro inside him. He felt Shiro’s finger stretching him, slowly but, it might just be enough.

Keith looked over his shoulder and gave Shiro a lazy grin. 

Shiro, with his free hand, began to pump his large cock, slowly at first, but gained into an easy rhythm. Hopefully those barbs weren’t as pointy as they looked. Shiro’s face knotted into one of focus and arousal. A familiar expression. When Shiro was satisfied with the level of slick he pulled his finger out and place his tip just at the entrance.

A gurgle of throaty noises, “ _ Are you ready?”  _ he seemed to ask.

“I’m good, go for it.” Keith sighed, Shiro lifted Keith’s hip up more for a better angle and slowly, gently pushed inside. “ _ God. _ ” Keith whimpered, it burned a little. Keith felt some cool wetness on his back.

Keith looked to see Shiro emptying the other half of the lube onto his cock and Keith’s ass. Probably a good idea. Shiro pushed in again. Keith felt his insides stretch and cling around Shiro’s cock. A growl of satisfaction from Shiro.

Keith remembered before, when he used to swear he could get more full than with Shiro’s cock inside. But Past Keith didn’t know shit.

Shiro thrust gently and Keith groaned. There wasn’t anywhere Shiro could lean down too or up to or any spot he could rub because Shiro was everywhere inside him. No nerve was left unrubbed when Shiro pounded into him again.

The barbs on Shiro’s dick created more of drag and rub on his insides then anything painful.

What was with these aliens that had abducted Shiro? Did they just make sexy monsters great for fucking?

Keith groaned, panting and squirmed with every thrust. Shiro’s breath grew ragged and laboured before a growly voice let out, “Ke-Keeeeef.” Keith was surprised, as, Shiro had just said something not unlike a word but was then surprised again by the sensation of warm, thick come filling him up. Shiro groaned and panted. This didn’t just last a moment, it lasted a full minute. Shiro still bucking into him wetly as he came.

Eventually, Shiro was spent, and slowly and stickily pulled out. 

Shiro rolled over next to Keith and caught his breath.

Keith lay on his back and spread his legs, “huh.” he touched some of the cum currently pouring out his ass, “It’s purple.” 

“Keeeeef.” Shiro growled, pouting almost.

Keith cuddled up to him. Remembering those moment from before.

_ “Keith stop, c’mon I want to snuggle”  _ Eventually turned into just him looking at Keith forlornly. Shiro was still the same really. Different, sure. But the same.

This was going to work. They were going to be happy again. Different, sure. But still Happy.

“I love you Shiro. I’m glad you back.” he closed his eyes.

Shiro growled in agreement. Happy to be back too.

**Author's Note:**

> Thanks for reading, remember to leave feedback, Also; This got some (NSFW!!) pre-fanart (https://razielim.tumblr.com/post/152540385628/if-shiro-came-back-to-earth-as-a-robeast-i-might)


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